Vertically integrated memory cell

ABSTRACT

A vertically integrated memory cell including a deep trench extending into a substrate, a trench capacitor located within the deep trench, and a vertical transistor at least partially embedded within the deep trench above the trench capacitor, the vertical transistor is in direct contact with and electrically coupled to the trench capacitor.

BACKGROUND

The present invention relates generally to semiconductor memory devices,and, more particularly, to a vertically integrated DRAM cell in which atransistor may be positioned directly above and vertically aligned to adeep trench capacitor.

A DRAM cell may typically include a deep trench capacitor electricallycoupled to a transistor. In general, a capacitor may include twoelectrodes separated by some barrier (e.g. node dielectric) used toisolate the two electrodes from one another. A deep trench capacitor maytypically be formed in a semiconductor-on-insulator substrate. Thesemiconductor-on-insulator substrate may have an SOI layer stacked ontop of a buried oxide layer and the buried oxide layer stacked on top ofa base substrate. The base substrate generally being n-doped silicon andthe SOI layer generally being p-doped silicon, or vice versa. A padlayer or hardmask may also be located atop thesemiconductor-on-insulator substrate. The deep trench capacitor may beformed through the pad layer and into all layers of thesemiconductor-on-insulator substrate. In such cases, the base substratemay act as one of the capacitor's two electrodes while a conductivelayer or an inner electrode may act as the other electrode.

The transistor may include a typical field effect transistor which maybe positioned on the SOI layer and adjacent to the deep trenchcapacitor. The transistor may be electrically coupled to the deep trenchcapacitor using a strap. More specifically, the inner electrode of thedeep trench capacitor may typically be electrically coupled to asource-drain region of the transistor.

SUMMARY

According to an embodiment of the present invention, a verticallyintegrated memory cell is provided. The vertically integrated memorycell may include a deep trench extending into a substrate, a trenchcapacitor located within the deep trench, and a vertical transistor atleast partially embedded within the deep trench above the trenchcapacitor, the vertical transistor is in direct contact with andelectrically coupled to the trench capacitor.

According to another embodiment of the present invention, a verticallyintegrated memory cell is provided. The vertically integrated memorycell may include a deep trench extending into a substrate, the deeptrench comprising a sidewall and a bottom; a trench capacitor locatedwithin the deep trench, the trench capacitor comprising a nodedielectric disposed along the sidewall and the bottom of the deep trenchand an inner electrode disposed on top of the node dielectric; and avertical transistor at least partially embedded within the deep trenchabove the trench capacitor, the vertical transistor comprising a channeland a gate, the channel is disposed within the deep trench above and indirect contact with the inner electrode of the trench capacitor, thegate is located within the substrate and surrounds the channel.

According to another embodiment of the present invention, a verticallyintegrated memory cell is provided. The vertically integrated memorycell may include a deep trench extending into asemiconductor-on-insulator substrate, the deep trench comprising asidewall and a bottom, the semiconductor-on-insulator substratecomprises an SOI layer, a buried oxide layer, and a base layer; theburied oxide layer is located below the SOI layer and above the baselayer, and the buried oxide layer electrically insulates the SOI layerfrom the base layer, a trench capacitor located within the deep trench,the trench capacitor comprising a barrier layer disposed along an entiresidewall and the bottom of the deep trench, a dielectric layer disposedon top of the barrier layer, and an inner electrode disposed on top ofthe dielectric layer, an upper surface of the inner electrode is belowthe SOI layer, and a vertical transistor at least partially embeddedwithin the deep trench above the trench capacitor, the verticaltransistor comprising a channel and a gate, the channel is disposedwithin the deep trench above and in direct contact with the innerelectrode of the trench capacitor, the gate is located within thesubstrate and surrounds the channel, and the barrier layer of the trenchcapacitor separates the gate from the channel.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description, given by way of example and notintend to limit the invention solely thereto, will best be appreciatedin conjunction with the accompanying drawings, in which:

FIGS. 1-6 illustrate the steps of a method of forming a verticallyintegrated DRAM cell according to an exemplary embodiment.

FIG. 1 depicts depositing a node dielectric and an inner electrodewithin a deep trench according to an exemplary embodiment.

FIG. 2 depicts recessing the node dielectric and the inner electrode toa predetermined depth according to an exemplary embodiment.

FIG. 3 depicts forming a first source-drain and a gate according to anexemplary embodiment.

FIG. 3A illustrates a cross section view, section A-A, of FIG. 3according to an exemplary embodiment.

FIG. 3B illustrates a cross section view, section A-A, of FIG. 3according to an exemplary embodiment.

FIG. 3C illustrates a cross section view, section A-A, of FIG. 3according to an exemplary embodiment.

FIG. 4 depicts forming a gate dielectric according to an exemplaryembodiment.

FIG. 5 depicts forming a channel and a second source-drain according toan exemplary embodiment.

FIG. 6 forming a contact level dielectric, a first contact, and a secondcontact according to an exemplary embodiment.

FIG. 7 depicts the vertically integrated DRAM cell according to anotherexemplary embodiment.

FIG. 8 depicts the vertically integrated DRAM cell according to anotherexemplary embodiment.

The drawings are not necessarily to scale. The drawings are merelyschematic representations, not intended to portray specific parametersof the invention. The drawings are intended to depict only typicalembodiments of the invention. In the drawings, like numbering representslike elements.

DETAILED DESCRIPTION

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it can be understood that the disclosed embodiments aremerely illustrative of the claimed structures and methods that may beembodied in various forms. This invention may, however, be embodied inmany different forms and should not be construed as limited to theexemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure will be thorough andcomplete and will fully convey the scope of this invention to thoseskilled in the art. In the description, details of well-known featuresand techniques may be omitted to avoid unnecessarily obscuring thepresented embodiments.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the disclosed structures andmethods, as oriented in the drawing figures. The terms “overlying”,“atop”, “on top”, “positioned on” or “positioned atop” mean that a firstelement, such as a first structure, is present on a second element, suchas a second structure, wherein intervening elements, such as aninterface structure may be present between the first element and thesecond element. The term “direct contact” means that a first element,such as a first structure, and a second element, such as a secondstructure, are connected without any intermediary conducting, insulatingor semiconductor layers at the interface of the two elements.

In the interest of not obscuring the presentation of embodiments of thepresent invention, in the following detailed description, someprocessing steps or operations that are known in the art may have beencombined together for presentation and for illustration purposes and insome instances may have not been described in detail. In otherinstances, some processing steps or operations that are known in the artmay not be described at all. It should be understood that the followingdescription is rather focused on the distinctive features or elements ofvarious embodiments of the present invention.

The present invention relates generally to semiconductor memory devices,and, more particularly to, a vertically integrated DRAM cell in which atransistor may be positioned directly above and vertically aligned to adeep trench capacitor. A vertically integrated DRAM cell may reducefabrication costs and increase device density. One way to fabricate thevertically integrate DRAM cell may include fabricating a vertical passgate transistor partially embedded in a deep trench directly above adeep trench capacitor. One way to fabricate the vertically integratedDRAM cell is described in detail below by referring to the accompanyingdrawings FIGS. 1-6.

Referring now to FIGS. 1-6, exemplary process steps of forming avertically integrated DRAM cell (hereinafter “DRAM cell”) in accordancewith an embodiment of the present invention are shown, and will now bedescribed in greater detail below. It should be noted that FIGS. 1-6 allrepresent a cross section view of a semiconductor structure 100(“structure”) depicting the fabrication of two DRAM cells.

Referring now to FIG. 1, a deep trench may be formed in asemiconductor-on-insulator substrate 102 (hereinafter “SOI substrate”).The SOI substrate 102 may include a base substrate 104, a buried oxidelayer 106 (hereinafter “BOX layer”) formed on top of the base substrate104, and an SOI layer 108 formed on top of the BOX layer 106. The BOXlayer 106 electrically insulates the SOI layer 108 from the basesubstrate 104. In addition, the SOI substrate 102 may have a pad nitridelayer 110 formed on a top surface of the SOI layer 108. The basesubstrate 104 may be made from any of several known semiconductormaterials such as, for example, a bulk silicon substrate. Othernon-limiting examples include silicon, germanium, silicon-germaniumalloy, silicon carbide, silicon-germanium carbide alloy, and compound(e.g. III-V and II-VI) semiconductor materials. Non-limiting examples ofcompound semiconductor materials include gallium arsenide, indiumarsenide, and indium phosphide. Typically the base substrate 104 may beabout, but is not limited to, several hundred microns thick. Forexample, the base substrate 104 may include a thickness ranging from 0.5mm to about 1.5 mm.

The BOX layer 106 may be formed from any of several dielectricmaterials. Non-limiting examples include, for example, oxides, nitridesand oxynitrides of silicon. Oxides, nitrides and oxynitrides of otherelements are also envisioned. In addition, the BOX layer 106 may includecrystalline or non-crystalline dielectric material. Moreover, the BOXlayer 106 may be formed using any of several methods. Non-limitingexamples include ion implantation methods, thermal or plasma oxidationor nitridation methods, chemical vapor deposition methods and physicalvapor deposition methods. In an embodiment, the BOX layer 106 may beabout 150 nm thick. Alternatively, the BOX layer 106 may have athickness ranging from about 10 nm to about 500 nm.

The SOI layer 108 may include any of the several semiconductor materialsincluded in the base substrate 104. In general, the base substrate 104and the SOI layer 108 may include either identical or differentsemiconducting materials with respect to chemical composition, dopantconcentration and crystallographic orientation. In an embodiment, thebase substrate 104 and the SOI layer 108 may include semiconductingmaterials that include at least different crystallographic orientations.Typically the base substrate 104 or the SOI layer 108 include a {108}crystallographic orientation and the other of the base substrate 104 orthe SOI layer 108 includes a {100} crystallographic orientation.Typically, the SOI layer 108 may have a thickness ranging from about 5nm to about 100 nm. Methods for making the SOI layer 108 are well knownin the art. Non-limiting examples include SIMOX (Separation byImplantation of Oxygen), wafer bonding, and ELTRAN® (Epitaxial LayerTRANsfer).

The pad nitride layer 110 may include an insulating material such as,for example, silicon nitride. The pad nitride layer 110 may be formedusing conventional deposition methods, for example, low pressurechemical vapor deposition (LPCVD), rapid thermal chemical vapordeposition (RTCVD), plasma enhanced chemical vapor deposition (PECVD),and high density plasma chemical vapor deposition (HDPCVD). The padnitride layer 110 may have a thickness ranging from about 10 nm to about500 nm. In an embodiment, the pad nitride layer 110 may be about 100 nmthick. Optionally, a thin (2 nm to 10 nm, preferably 5 nm) thermal oxidelayer (not shown) may be formed on the SOI layer 108 prior to formingthe pad nitride layer 110.

A deep trench may then be formed using known patterning techniques, suchas for example, a lithography process followed by etching process. Theterm “deep trench” denotes a trench formed in a semiconductor substratehaving a sufficient depth to form a capacitor. As such, a deep trenchmay typically denote a trench having a depth equal to or greater than 1micron, whereas a shallow trench may typically refer to a trench havinga depth less than 1 micron. While the present embodiment may bedescribed with a deep trench, the present embodiment may be employedwith a trench having any depth into the SOI substrate 102. Suchvariations are explicitly contemplated herein.

The lithography technique may include applying a photoresist (not shown)to an upper surface of the pad nitride layer 110, exposing thephotoresist to a desired pattern of radiation and developing the exposedphotoresist utilizing a conventional resist developer. The pattern inthe photoresist may then be transferred to the pad nitride layer 110 andthe SOI substrate 102 using one or more dry etching techniques to formthe deep trench. Suitable dry etching techniques may include, but arenot limited to: reactive ion etching (RIE), ion beam etching, plasmaetching, or laser ablation. The patterned photoresist may then beremoved by resist stripping after etching has been completed. In anembodiment, an optional hardmask layer, such as an oxide (not shown),may be deposited on top of the pad nitride layer 110 to facilitate theformation of the deep trench. The hardmask layer may generally beremoved after the formation of the deep trench.

Next, a deep trench capacitor 112 may be formed in the deep trenchaccording to know techniques. The deep trench capacitor 112 may includea buried plate 114, a node dielectric 116, and an inner electrode 118.The buried plate 114 and the inner electrode 118 may serve as the twoelectrical conductors and the node dielectric 116 may serve as theinsulator between the two conductors.

An optional blanket doping technique may be used to form the buriedplate 114. Suitable doping techniques may include, but are not limitedto, ion implantation, gas phase doping, plasma doping, plasma immersionion implantation, cluster doping, infusion doping, liquid phase doping,solid phase doping, or any suitable combination of those techniques. Inone embodiment, dopants may be implanted by one or more rounds of angledion implantation to dope the sidewalls and the bottom of the deeptrench. In doing so, dopants may be introduced into the base substrate104 to form the buried plate 114. Typical dopants may include As, P, Sb,B, Ga, and In. The pad nitride layer 110 may protect the top surface ofthe SOI layer 108 from being doped by the ion implantation. Because ofthe pad nitride layer 110, no special techniques may be required to maskor protect surrounding areas of the SOI layer 108 from the implantationof unwanted dopants. It should be noted that the blanket dopingtechnique above may not be required, and in such cases the doped basesubstrate 104 may function as the buried plate 114.

With continued reference to FIG. 1, the node dielectric 116 may then beformed within the deep trench, and directly on the buried plate 114 andalong the sidewalls of the pad nitride layer 110. The node dielectric116 may include a dielectric material such as silicon oxide, siliconnitride, or silicon oxynitride. The thickness of the node dielectric 116may range from about 2 nm to about 6 nm. Alternately, the nodedielectric 116 may include a high-k material having a dielectricconstant greater than the dielectric constant of silicon nitride, whichis about 7.5. Exemplary high-k materials include HfO₂, ZrO₂, La₂O₃,Al₂O₃, TiO₂, SrTiO₃, LaAlO₃, Y₂O₃, HfO_(x)N_(y), ZrO_(x)N_(y),La₂O_(x)N_(y), Al₂O_(x)N_(y), TiO_(x)N_(y), SrTiO_(x)N_(y),LaAlO_(x)N_(y), Y₂O_(x)N_(y), a silicate thereof, and an alloy thereof.Each value of x may independently range from about 0.5 to about 3 andeach value of y may independently range from 0 to about 2. In this case,the thickness of the node dielectric 116 may range from about 2 nm toabout 10 nm, although lesser and greater thickness may be contemplated.In an embodiment, the node dielectric 116 may include a combination ofmultiple materials. In an embodiment, the node dielectric 116 includesHfO_(x) deposited by ALD with a thickness of about. According to analternative embodiment, the node dielectric 116 may include more thanone layer as described below with reference to FIG. 8.

Next, the inner electrode 118 may be formed by depositing a conductiveor semi-conductive material on the inner walls of the node dielectric116 according to known techniques. The inner electrode 118 may be formedby known suitable deposition techniques, for example, chemical vapordeposition (CVD), physical vapor deposition (PVD), atomic layerdeposition (ALD), or low pressure chemical vapor deposition (LPCVD). Theinner electrode 118 may be a doped or un-doped semiconductor material, ametal, or some combination thereof. In the present embodiment, the innerelectrode 118 may be an un-doped semiconductor material, such as, forexample, un-doped polysilicon. If the inner electrode 118 is a dopedsemiconductor material, the doped semiconductor material may include anymaterial listed above for the base layer 104. The dopants may be ap-type dopant or an n-type dopant.

If the inner electrode 118 is an elemental metal, exemplary elementalmetals may include Ta, Ti, Co, and W. Alternatively, inner electrode 118may be a conductive metallic alloy, and exemplary conductive metallicalloys may include a mixture of elemental metals, a conductive metallicnitride such as TiN, ZrN, HfN, VN, NbN, TaN, WN, TiAlN, TaCN, and analloy thereof. It should be noted that the inner electrode 118, whileonly depicted as a single layer, may include a plurality of layers ofthe same or different materials.

Excess material that may be deposited outside the deep trench, may beremoved by a recess etch or chemical mechanical planarization. The nodedielectric 116 or the pad nitride layer 110 may be used to sense anendpoint during the recess etch, or alternately, may be employed as astopping layer during the chemical mechanical planarization.

Referring now to FIG. 2, the node dielectric 116 and the inner electrode118 may then be recessed to a predetermined depth within the buriedoxide layer 106 below the SOI layer 108 to create an opening 120.However, although the exact depth is not critical, any depth below theSOI layer 108 may be sufficient. More specifically, an entire sidewallof the SOI layer 108 may preferably be exposed and the node dielectric116 may remain above the interface between the base substrate 104 andthe BOX layer 106 to prevent a short circuit between the buried plate114 and the inner electrode 118. In one embodiment, the inner electrode118 may be recessed such that an upper surface of the inner electrode118 may be substantially flush with the interface between the buriedoxide layer 106 and the SOI layer 108. A conventional etch process suchas, for example, plasma etch, reactive ion etch (RIE), or chemicaldownstream etch, can be used to recess the node dielectric 116 and theinner electrode 118.

In an embodiment, the node dielectric 116 and the inner electrode 118are recessed simultaneously using the same etching technique. In anembodiment, the node dielectric 116 and the inner electrode 118 arerecessed one after the other using different etching techniques, oralternatively, the same etching technique with different chemistries. Inan embodiment, the node dielectric 116 and the inner electrode 118 areboth recessed using a reactive ion etching (RIE) technique.

In an embodiment, the node dielectric 116 and the inner electrode 118may be recessed to the same depth, or about the same depth, asillustrated on the right side of the figures. In another embodiment, thenode dielectric 116 and the inner electrode 118 may be recessed todifferent depths, as illustrated on the left side of the figures. Insuch cases, either the node dielectric 116 or the inner electrode 118may be recessed deeper than the other depending on design. In all cases,the node dielectric 116 is not recessed below the buried oxide layer 106for reasons mentioned above. If, however, the node dielectric 116 isrecessed below the buried oxide layer 106, an additional insulatinglayer may be required to prevent a short circuit between the buriedplate 114 and the inner electrode 118.

Referring now to FIGS. 3 and 3A, a first source-drain 122 and a gate 124may be formed according to known techniques, as shown. FIG. 3A is across section view, section A-A, of FIG. 3. In an embodiment, the firstsource-drain 122 and the gate 124 may be fabricated by doping an upperportion of the inner electrode 118 and a portion of the SOI layer 108exposed within the deep trench, respectively, using any implanttechnique known in the art. For example, an ion implant technique may beused to introduce dopants into the upper portion of the inner electrode118 and the portion of the SOI layer 108. More specifically, the upperportion of the inner electrode 118 exposed at a bottom of the opening120 and the portion of the SOI layer 108 immediately surrounding theopening 120 may be doped with N-type or P-type dopants to create thefirst source-drain 122. It should be noted that the dopant type may beselected based on the desired device characteristics. Also, the gate 124may preferably have a ring shape and surround the opening 120, asillustrated in FIG. 3A. It should be noted that subsequent heating orannealing techniques may cause the dopants used to create thesource-drain 122 may further diffuse into a semiconductor materialformed later directly on top of the source-drain 122.

According to another alternative embodiment not shown, either or both ofthe first source-drain 122 and the gate 124 may include a metallicmaterial or a silicide. In general, the metallic material or thesilicide may be formed in addition to and on top of the doped regions(122, 124) described above. In some instances, the doped regions (122,124) may be recessed to accommodate the addition of the metallicmaterial or silicide.

According to another alternative embodiment not shown, the firstsource-drain 122 may be formed by growing a doped semiconductormaterial, such as silicon germanium, directly on top of the innerelectrode 118. In such cases, the inner electrode 118 may be recessedfurther than above to accommodate the additional height of growing thesemiconductor material on top of the inner electrode 118. Similarconfigurations to those of the structure 100 in FIG. 3 are envisioned.

In general, the first source-drain 122 and the gate 124 may have anappropriate shape and size to achieve the desired device characteristicswhile conforming to the structural limitations presented herein.Preferably, the gate 124 may have a shape and size sufficient to form acontact thereto. For example, the ring shape of the gate 124 may have asufficient thickness to subsequently form an electrical connection. SeeFIG. 6. As such, a thickness (t) of the ring shape of the gate 124 mayor may not be substantially uniform.

Referring now to FIG. 3B, a cross section view, section A-A, of FIG. 3is shown according to another embodiment. In another embodiment, thethickness (t) of the ring shape (FIG. 3A) of the gate 124 may beproportionally thicker in only one area to specifically accommodate thesubsequently formed electrical connection to the gate 124.

Referring now to FIG. 3C, a cross section view, section A-A, of FIG. 3is shown according to another embodiment. In another embodiment, thethickness (t) of the ring shape (FIG. 3A) of the gate 124 may besubstantially uniform with the addition of a “leg” or “extension” whichmay be fabricated specifically to accommodate the subsequently formedelectrical connection to the gate 124. The “leg” or “extension” may befabricated at the same time or subsequently using a similar implanttechnique as is used to form the gate 124, as described above withreference to FIG. 3.

Referring now to FIG. 4, a gate dielectric 128 may be formed along asidewall of the opening 120, according to known techniques. The gatedielectric 128 can be formed by a deposition process such as, forexample, chemical vapor deposition (CVD), plasma-assisted CVD, atomiclayer deposition (ALD), evaporation, reactive sputtering, chemicalsolution deposition or other like deposition processes. Alternatively,the gate dielectric 128 can be formed by a thermal growing process suchas, for example, oxidation, nitridation or oxynitridation. The gatedielectric 128 may also be formed using any combination of the aboveprocesses.

The gate dielectric 128 may include an insulating material including,but not limited to: an oxide, a nitride, an oxynitride or a silicateincluding metal silicates and nitrided metal silicates. In anembodiment, the gate dielectric 128 may include an oxide such as, forexample, SiO₂, HfO₂, ZrO₂, Al₂O₃, TiO₂, La₂O₃, SrTiO₃, LaAlO₃, andmixtures thereof. The thickness of the gate dielectric 128 may vary, buttypically may have a thickness ranging from about 0.5 nm to about 10 nm.More preferably the gate dielectric 128 may have a thickness rangingfrom about 0.5 nm to about 3 nm.

It should be noted that depending on the chosen fabrication techniquethe gate dielectric 128 may need to be removed from a bottom of theopening 120 to expose the first source-drain 122. Furthermore, the gatedielectric 128 of the present embodiment may extend from an uppersurface of the pad nitride layer 110 down to the bottom of the opening120 in contact with the node dielectric 116. In an embodiment where athermal growing process is used, the gate dielectric 128 may be alignedonly with the SOI layer 108 and neither the buried oxide layer 106 northe pad nitride layer 110.

Referring now to FIG. 5, a channel 130 may be formed within the opening120 (FIG. 4) above and in direct contact with the first source-drainregion 122 according to known techniques. The channel 130 may be formedfirst by filling the opening 120 (FIG. 4) with an un-doped semiconductormaterial and then recessing the un-doped semiconductor material to adesired depth. The channel 130 may be formed using any known depositiontechnique such as, for example, chemical vapor deposition (CVD),plasma-assisted CVD, atomic layer deposition (ALD), evaporation,reactive sputtering, chemical solution deposition or other likedeposition processes. In an embodiment, the channel 130 may include anyun-doped semiconductor material, such as, for example, un-dopedpolysilicon. Alternatively, the channel 130 may be made from asemiconductor material which may be doped opposite that of thesource-drains 122, 132. In general, the channel 130 may have acylindrical shape extending from the first source-drain 122 up to aboutthe interface between the SOI layer 108 and the pad nitride layer 110.As previously mentioned, it should be noted that the dopants used tocreate the source-drain 122 may further diffuse into the semiconductormaterial of the channel 130 expanding its shape and size as illustrated.

In an embodiment, the channel 130 may generally be aligned with the SOIlayer 108. More specifically, the channel 130 may generally be alignedwith the gate 124. Stated differently, a relative height (H₁) of thechannel 130 may be about equal to a relative height (H₂) of the gate124. Alternatively, the channel 130 may have a relative height (H₁)greater than or less than the relative (H₂) height of the gate 124. Itshould be noted that the relative height (H₂) of the gate 124 may besubstantially similar to the thickness of the SOI layer 108. Also, itshould be noted that the relative height (H₁) of the channel 130, may bemeasured from an upper surface of the first source-drain 122 to a lowersurface of a second source-drain (discussed below). Unlike aconventional planar transistor where a gate is positioned directly abovea channel, the gate 124 in the present embodiment may preferablysurround the channel 130. Also, as with most field effect transistors,the gate dielectric 128 may separate or insulate the gate 124 from thechannel 130.

Next, a second source-drain 132 may be formed above and in directcontact with the channel 130, according to known techniques. The secondsource-drain 132 may be formed using similar techniques as describedabove with reference to the first source-drain 122. The secondsource-drain 132 may include a doped semiconductor material similar tothat of the first source-drain 122. As mentioned above, the un-dopedsemiconductor material of the channel 130, in most cases, may berecessed before forming the second source-drain region 132. Also likeabove, the second source-drain 132 may alternatively be formed bygrowing a doped semiconductor material, such as, for example, silicongermanium.

With continued reference to FIG. 5, the structure 100 is shown with twocompleted DRAM cells, one on the left side of the figure and one on theright side of the figure. Each DRAM cell may include a field effecttransistor 134 (hereinafter “FET”) positioned directly above andvertically aligned to the deep trench capacitor 112. The FET 134 may bealternatively referred to as a vertical pass gate transistor. The FET134 of the present embodiment may include the first source-drain 122,the second source-drain 132, and the gate 124. In the presentembodiment, the FET 134 may be electrically coupled to the deep trenchcapacitor 112 to form the DRAM cell. More specifically, the innerelectrode 118 of the deep trench capacitor 112 may be electricallycoupled to the first source-drain 122 of the FET 134.

It should be noted each of the DRAM cells illustrated in FIG. 5represent two alternative configurations. More specifically, thedifference between the alternative configurations relates to recessingthe node dielectric 116 and the inner electrode 118, as described abovewith reference to FIG. 2.

In an embodiment, as illustrated by the DRAM cell on the right side ofthe figures, the node dielectric 116 and the inner electrode 118 may berecessed to a substantially similar depth. In such cases, the channel130 may be subsequently formed above and in direct contact with thefirst source-drain 122. More specifically, a lower surface of thechannel 130 may be in direct contact with an upper surface of the firstsource-drain 122.

In another embodiment, as illustrated by the DRAM cell on the left sideof the figures, the node dielectric 116 may be recessed below the innerelectrode 118. In such cases, not only the upper surface of the firstsource-drain 122 may be exposed, but a sidewall may also be exposed. Assuch, the semiconductor material of the channel 130 can partially wraparound and contact the sidewall in addition to the upper surface of thefirst source-drain 122; however, as mentioned above, the source-drain122 may expand to include any semiconductor material of the channel 130in contact with the sidewall of the source-drain 122.

According to another embodiment, a similar configuration to the DRAMcell depicted on the right side of the figures may be achieved by firstrecessing the inner electrode 118 deeper than the node dielectric 116and subsequently forming the first source-drain 122 by growing ordepositing a doped semiconductor material on an exposed upper surface ofthe inner electrode 118.

Referring now to FIG. 6, the final structure 100 is shown with acontact-level dielectric 136 deposited on top of the structure above theDRAM cells according to known techniques. In an embodiment, thecontact-level dielectric 136 may include, but is not limited to, amaterial made from, a nitride, an oxide, a carbide, or any combinationof these materials. In an embodiment, the contact-level dielectric 136may include an oxide deposited using a CVD technique. The contact-leveldielectric 136 may have a thickness ranging from about 20 nm to 100 nm,although a thickness of the contact-level dielectric 136 less than 20 nmor greater than 100 nm may be acceptable. The contact-level dielectric136 may be planarized using a chemical mechanical polishing techniqueafter being formed on top of the structure 100.

Next, one or more contact trenches may then be formed by etching throughthe contact-level dielectric 136 to make electrical connections with theDRAM cells formed in the SOI substrate 102. A first contact trench mayextend from a top surface of the contact-level dielectric 136 down tothe second source-drain 132. A second contact trench may extend from atop surface of the contact-level dielectric 136 down to the gate 124.

With continued reference to FIG. 6, a conductive material may bedeposited to fill the first and second contact trenches and form a firstcontact 138 and a second contact 140. The conductive material mayinclude any material having a high electrical conductivity. In oneembodiment, the conductive material can include, for example, tungsten,copper, aluminum, silver, gold, alloys thereof, and any suitablecombination thereof. The conductive material can be deposited by anysuitable technique, including but not limited to, for example, atomiclayer deposition (ALD), molecular layer deposition (MLD), chemical vapordeposition (CVD), in-situ radical assisted deposition, metalorganicchemical vapor deposition (MOCVD), molecular beam epitaxy (MBE),physical vapor deposition (PVD), sputtering, plating, evaporation, ionbeam deposition, electron beam deposition, laser assisted deposition,chemical solution deposition, or any combination thereof. The thickness,or depth, of the first and second contacts 138, 140 may range from about20 nm to about 100 nm, although lesser and greater thicknesses may alsobe contemplated. After deposition, a planarization process, such as, forexample, chemical mechanical polishing, may be performed to remove anyexcess conductive material above the contact-level dielectric 136.

Another embodiment by which to fabricate the vertically integrated DRAMcell is described in detail below by referring to FIG. 7. In the presentembodiment, a channel 202 may, in general, have a tubular shape whichmay be filled with an insulating material, as described below.

FIG. 7 illustrates a final structure 200 in accordance with embodimentsof the present invention. Like above, the figure is a cross section viewof a portion of a semiconductor wafer. It should be noted that thefollowing stages of fabrication of the present embodiment describedbelow may generally replace those fabrication stages described abovewith reference to FIG. 5. As such, the following description maycontinue after the description of FIG. 4, and subsequently resume withthe description of FIG. 6.

Referring now to FIG. 7, the channel 202 may be formed within theopening 120 (FIG. 4) above and in direct contact with the firstsource-drain region 122 according to known techniques. The channel 202may be substantially similar to the channel 130 described above withreference to FIG. 5. In the present embodiment, the channel 202 may beformed by conformally depositing a liner having a thickness within theopening 120 (FIG. 4), as illustrated. As such, the channel 202 may havea substantially tubular shape. Like the channel 130 described above, thechannel 202 depicted on the left side of the figure may benefit fromincrease contact area with the first source-drain 122.

After depositing the liner to form the channel 202, an insulatingmaterial 204, such as, for example, silicon oxide or other suitableinsulating materials, may be deposited to substantially fill the opening120 (FIG. 4). In the present embodiment, the insulating material 204 maythen be recessed selective to the channel 202 according to knowntechniques in preparation for the formation of the second source-drain132, as described above. Finally, fabrication of the structure 200 maycontinue according to the techniques described above with reference toFIG. 6.

Another embodiment by which to fabricate the vertically integrated DRAMcell is described in detail below by referring to FIG. 8. FIG. 8illustrates a final structure 300 in accordance with embodiments of thepresent invention. In the present embodiment, the node dielectric 116may include more than one layer. More specifically, a barrier layer 116a and a dielectric layer 116 b may be deposited within the deep trenchto form the node dielectric 116. The barrier layer 116 a may include adielectric material such as silicon oxide, silicon nitride, or siliconoxynitride. The dielectric layer 116 b may include, for example, ahigh-k material having a dielectric constant greater than the dielectricconstant of silicon nitride, which is about 7.5, specific examples ofwhich are included above. In the present embodiment, the barrier layer116 a may substantially remain and function as a gate dielectric. Insuch cases, the gate dielectric 128 described above with reference toFIG. 4 may not be required. The dielectric layer 116 b may be recessedand/or configured similar to the node dielectric 116 as described above.

In all embodiments, the FET 134 may be positioned directly above andvertically aligned to the deep trench capacitor 112 to form thevertically integrated DRAM cells. Such a configuration conservesvaluable substrate area thereby substantially increasing the possibleDRAM cell density.

A typical DRAM cell may generally include a field effect transistorpositioned adjacent to a deep trench capacitor. If, for exemplarypurposes, a field effect transistor and a deep trench capacitor eachconsumed the same amount of substrate area, positioning the FET 134directly above the deep trench capacitor 112, as described in detailabove, would reduce the DRAM cells footprint by half.

In addition to saving valuable substrate area, the vertically integratedDRAM cell proposed above may be fabricated in fewer steps than aconventional DRAM cell. Fewer fabrication steps may be achieved bypartially embedding the FET 134 within the deep trench as describedabove. Fewer steps means faster fabrication time and lower fabricationcost. In addition, the embodiments disclosed above are particularlyunique in that the channel 130 of the FET 134 is fabricated frompolysilicon which is generally not used in typical FET construction forits poor electron mobility leading to poor device performance. In thepresent case, performance may be sacrificed for increased layoutdensity. Therefore, anyone looking to make a high performance devicewould not consider polysilicon as a suitable channel material and wouldotherwise not be inclined to fabricate the structures, or any variationthereof, disclosed above.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiment, the practical application or technicalimprovement over technologies found in the marketplace, or to enableother of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A vertically integrated memory cell comprising: adeep trench extending into a semiconductor-on-insulator substratecomprising an SOI layer, a buried oxide layer, and a base layer; theburied oxide layer is located below the SOI layer and above the baselayer, and the buried oxide layer electrically insulates the SOI layerfrom the base layer; a trench capacitor located within the deep trench;and a vertical transistor at least partially embedded within the deeptrench above the trench capacitor, the vertical transistor is in directcontact with and electrically coupled to the trench capacitor, and agate of the vertical transistor is located within the SOI layer andsurrounds the deep trench.
 2. The vertically integrated memory cell ofclaim 1, wherein an upper surface of an inner electrode of the trenchcapacitor is below a bottom surface of the SOI layer.
 3. The verticallyintegrated memory cell of claim 1, wherein the vertical transistorcomprises a channel disposed within the deep trench above and in directcontact with an inner electrode of the trench capacitor, the channelhaving a generally cylindrical shape.
 4. The vertically integratedmemory cell of claim 1, wherein the vertical transistor comprises achannel disposed within the deep trench above and in direct contact withan inner electrode of the trench capacitor, the channel having agenerally tubular shape.
 5. The vertically integrated memory cell ofclaim 1, wherein the vertical transistor comprises a channel and asource-drain, the channel is disposed within the deep trench above andin direct contact with an inner electrode of the trench capacitor, thesource-drain is above and in direct contact with the channel, andextends above the semiconductor-on-insulator substrate.
 6. Thevertically integrated memory cell of claim 1, wherein the verticaltransistor comprises a channel and a source-drain, the channel isdisposed within the deep trench above and in direct contact with aninner electrode of the trench capacitor, the source-drain comprises anupper portion of the inner electrode.
 7. The vertically integratedmemory cell of claim 1, wherein the vertical transistor comprises achannel and a gate dielectric, the channel is disposed within the deeptrench above and in direct contact with an inner electrode of the trenchcapacitor, the gate dielectric is disposed along and in direct contactwith a sidewall of the deep trench above the trench capacitor andinsulates the channel from the gate, the gate dielectric extendsvertically from an uppermost surface of a node dielectric of the trenchcapacitor to a top surface of the SOI layer.
 8. A vertically integratedmemory cell comprising: a deep trench extending into asemiconductor-on-insulator substrate comprising an SOI layer, a buriedoxide layer, and a base layer; the buried oxide layer is located belowthe SOI layer and above the base layer, and the buried oxide layerelectrically insulates the SOI layer from the base layer, the deeptrench comprising a sidewall and a bottom; a trench capacitor locatedwithin the deep trench, the trench capacitor comprising a nodedielectric disposed along the sidewall and the bottom of the deep trenchand an inner electrode disposed on top of the node dielectric; and avertical transistor at least partially embedded within the deep trenchabove the trench capacitor, the vertical transistor comprising a channeland a gate, the channel is disposed within the deep trench above and indirect contact with the inner electrode of the trench capacitor, thegate is located within the SOI layer and surrounds the deep trench. 9.The vertically integrated memory cell of claim 8, wherein an uppersurface of the inner electrode of the trench capacitor is below a bottomsurface of the SOI layer.
 10. The vertically integrated memory cell ofclaim 8, wherein the channel has a generally cylindrical shape.
 11. Thevertically integrated memory cell of claim 8, wherein the channel isdisposed along the sidewall of the deep trench and has a generallytubular shape.
 12. The vertically integrated memory cell of claim 8,further comprising: a source-drain above and in direct contact with thechannel, and extending above the semiconductor-on-insulator substrate.13. The vertically integrated memory cell of claim 8, furthercomprising: a source-drain comprising an upper portion of the innerelectrode.
 14. The vertically integrated memory cell of claim 8, whereinthe node dielectric comprises a barrier layer and a dielectric layer,wherein an uppermost surface of the barrier layer is substantially flushwith a top surface of a source-drain directly above the channel, and anuppermost surface of the dielectric layer is above a top surface of thebase layer and below a top surface of the buried oxide layer.
 15. Thevertically integrated memory cell of claim 8, further comprising: a gatedielectric disposed along and in direct contact with the sidewall of thedeep trench, the gate dielectric extends vertically from an uppermostsurface of the node dielectric to a top surface of the SOI layer andinsulates the channel from the gate.
 16. A vertically integrated memorycell comprising: a deep trench extending into asemiconductor-on-insulator substrate, the deep trench comprising asidewall and a bottom, the semiconductor-on-insulator substratecomprises an SOI layer, a buried oxide layer, and a base layer; theburied oxide layer is located below the SOI layer and above the baselayer, and the buried oxide layer electrically insulates the SOI layerfrom the base layer; a trench capacitor located within the deep trench,the trench capacitor comprising a barrier layer disposed along an entiresidewall and the bottom of the deep trench, a dielectric layer disposedon top of the barrier layer, and an inner electrode disposed on top ofthe dielectric layer, an upper surface of the inner electrode is below abottom surface of the SOI layer, and above a top surface of the baselayer; and a vertical transistor at least partially embedded within thedeep trench above the trench capacitor, the vertical transistorcomprising a channel and a gate, the channel is disposed within the deeptrench above and in direct contact with the inner electrode of thetrench capacitor, the gate is located within the SOI layer and surroundsthe channel, and the barrier layer of the trench capacitor separates thegate from the channel.
 17. The vertically integrated memory cell ofclaim 16, wherein the channel has a generally cylindrical shape.
 18. Thevertically integrated memory cell of claim 16, wherein the channel isdisposed along the sidewall of the deep trench and has a generallytubular shape surrounding an insulating material directly above theinner electrode and directly below a source-drain.
 19. The verticallyintegrated memory cell of claim 16, further comprising: a source-drainabove and in direct contact with the channel, and extending above thesemiconductor-on-insulator substrate.
 20. The vertically integratedmemory cell of claim 16, further comprising: a source-drain comprisingan upper portion of the inner electrode.